Rewrite action version check

The crucial missing component was cding into the preview repository
after bare cloning it. Without that, this script has been checking the
version of the user's project repository this entire time.

action.yml

@@ -110,9 +110,9 @@ runs:
       shell: bash
 
     - name: Determine action version
-      run: >-
-        $GITHUB_ACTION_PATH/lib/find-current-git-tag.sh
-        -p $actionrepo -f $actionref
+      run: |
+        action_version=$("${{ github.action_path }}/lib/find-current-git-tag.sh" -p $actionrepo -f $actionref)
+        echo "action_version=$action_version" >> "$GITHUB_ENV"
       shell: bash
 
     - name: Determine auto action

lib/find-current-git-tag.sh

@@ -21,14 +21,14 @@ if [ -z "$github_repository" ] || [ -z "$git_ref" ]; then
   helpFunction
 fi
 
-echo >&2 "Determining preview action version"
+echo >&2 "Determining Git tag for $github_repository/$git_ref"
+
 echo >&2 "Cloning repository $github_repository at ref $git_ref"
-if git clone --bare --single-branch --branch "$git_ref" "https://github.com/$github_repository" bare_pr_preview; then
-  echo >&2 "Finding most specific tag matching tag $git_ref"
-  action_version=$(git describe --tags --match "v*.*.*" || git describe --tags || git rev-parse HEAD)
-  echo >&2 "Found $action_version"
-  echo "action_version=$action_version" >>"$GITHUB_ENV"
-else
-  echo >&2 "Clone failed; using truncated ref as action version"
-  echo "action_version=${git_ref:0:9}" >>"$GITHUB_ENV"
-fi
+git clone --bare --single-branch --branch "$git_ref" "https://github.com/$github_repository" bare_pr_preview
+
+cd bare_pr_preview || exit 1
+
+action_version=$(git describe --tags --match "v*.*.*" || git describe --tags || git rev-parse HEAD)
+
+echo "$action_version"
+exit 0